Personal cleansers delight users with rich lather and a fresh, clean feel for hair and skin. Most personal cleansers—shampoos, body washes, facial cleansers, liquid soaps, and the like—are formulated with a combination of surfactants. A primary anionic surfactant provides cleansing and foaming properties to allow fast, complete removal of soils from skin and hair. Alkyl sulfates and alkyl ether sulfates are ubiquitous in this role because they provide rich foam and are cost effective. A relatively minor proportion of a “secondary” surfactant is usually included to build viscosity, improve solubility, stabilize the foam, enhance foaming, or improve mildness. The most common secondary surfactants are fatty alkanolamides (e.g., cocamide MEA, lauramide MEA, or cocamide DEA), and betaines (e.g., cocamidopropyl betaine). Formulations free of cocamide MEA or cocamide DEA have become desirable to formulators to reduce irritation or to avoid the need for warnings required by certain government regulations such as California's Proposition 65.
Fatty alkyl N,N-dialkylamides, especially C8-C10 alkyl N,N-dimethylamides, are well-known solvents. Stepan Company, for instance, sells HALLCOMID® M-10 and HALLCOMID® M-8-10 for use as solvents in industrial degreasing, coatings, and agricultural formulations. The N,N-dialkylamides are not generally used for personal care applications except as solubilizers for sunscreen actives (see, e.g., U.S. Pat. Nos. 4,506,051; 6,485,713; 7,790,146; and 8,153,105 and PCT Int. Appl. WO 2007/085568) or as components of deodorant sticks (see U.S. Pat. Appl. Publ. No. 2003/0215472). PCT Int. Appl. WO 2013/052545 teaches to use fatty alkyl N,N-dialkylamides to help solubilize apigenin in compositions used to treat hair thinning or greying. Fatty alkyl N,N-dialkylamides have been proposed as soap curd dispersants for laundry detergents (see, e.g., U.S. Pat. No. 3,843,543) or as part of a light-duty dish detergent (see U.S. Pat. No. 3,676,372). Thus, compositions comprising C8-C14 alkyl N,N-dialkylamides and intended for use as personal cleansers are apparently unknown.
Recently, monounsaturated fatty alkyl N,N-dimethylamides and monounsaturated fatty alkanolamides were tested and found to have good foaming and viscosity-building properties (see PCT Int. Appl. No. WO 2012/061094).
A desirable surfactant or blend will be sensitive to the amount of added viscosity modifier. Usually, a salt (e.g., sodium chloride) is added to increase viscosity. Preferably, the amount of added salt needed to achieve a favorable viscosity profile is minimized. However, with many primary anionic surfactants (e.g., alpha-olefin sulfonates, alkyl ether sulfates, fatty sulfosuccinates, fatty sulfoacetates, and their mixtures), building viscosity with the popular alkanolamides or betaines can be difficult or may require a relatively high proportion of salt.
Good surfactants are not necessarily good solubilizers. This is a particular concern in personal cleansers because the industry uses a wide variety of fragrances, essential oils, and other components having diverse chemical structures. Many of these materials are hydrophobic and difficult to solubilize in a highly aqueous mixture.
Still needed are surfactants or surfactant blends that can deliver good foaming, mildness, and an improved viscosity build profile to personal cleansers. Liquid surfactants or blends, particularly products that can be formulated at high actives levels, are also needed. Particularly valuable are surfactants or blends that could be formulated at any actives level up to 100% actives. Surfactants or blends having the ability to solubilize cleanser components, including a wider variety of fragrances and high levels of fragrances (e.g., >2 wt. %), are also needed. In addition, the industry would benefit from the availability of MEA or DEA-free formulations that build viscosity readily with even challenging anionic surfactants.